Oxidizing catalyst



Patented Dec. s, 1933 v a a 1,937,689

UNITED STATES PATENT OFFICEY OXIDIZING CATALYST Joseph C. W. Frazer,Baltimore, Md.

No Drawing. Application July 23, 1929 Serial No. 380,453

7 claims. (01. 23-234) This invention relates to catalysts, andespecriterionof purity is attained, coupled with cially to catalystscapable of causing oxidizing proper physical state, as will beunderstood, the reactions. materials are highly active oxidizing.catalysts in It is well known that various single metallic dry gasatmospheres, and their life is apparc oxides are satisfactory agents forcatalytically ently unlimited. The proper degree of purity 60 oxidizinggases and vapors at elevated temperamay also be shown as follows. Inprior work tures. Although some of these oxides, for inalong theselines, the materials were washed unstance, oxides of cobalt or nickel,may show some til the wash water gave no test for impurity, it catalyticactivity at reduced temperatures, their being considered that the oxidewas then abso- 10 lives have been short, or their continued converlutelypure. However, I find that the oxides thus 65 sion eiiiciencies werelow, and because as preprepared will give a positive test for impuritypared for such use these oxides have been thought when dissolved inacid. on the'other hand, catato be perfectly pure, their deficiency incatalytic lysts provided by the invention give no test for activity atlow temperatures has been thought to impurity when dissolved in acid,thus showing be inherent. adequate purity for the purposes of the inven-The object of the invention is to provide a catation. lyst comprising anoxide of a single metal, which The invention contemplates as itspreferred is highly and continuously active for vapor phase embodimentoxide of cobalt, but it is likewise apoxidation at reduced temperatures,possesses unplicable to oxide of nickel. The most recent de-" limitedlife when used in dry gas atmosphere. terminations show each of thesemetals to have 75 may be easily and economically prepared in a an atomicweight between 58 and 59, and this variety of ways, and which may bereadily revivicharacteristic will be used to refer concisely to fled ifnecessary. e the catalysts comprised by the invention. The

I- have found that, co t ary to the p va n catalysts may beprepared in.a variety of ways,

beliefs, oxide of nickel, or oxide of cobalt, were hi h together ith thcharacteristics of the g ineflicientas low temperature catalystsbecause, catalysts, may best be described in the followdespite thecareful purification which has previing specific examples of itspreferred embodiously been practiced, they contained an amount merit, ofimpurities suflicient to reduce their catalytic Example 1 mti of 211grams r cobalp w er wo ds. ove ou d at b p tous nitrate [C0(NO3)2.6H20]in 200 cc. of cold D rin these ma erial in a higher State Of P y wateris added slowly to 100 grams of sodium hytha heretofore. h r i P e a t ydroxide (NaOH) made up to a 1.3 Sp. g. solution. mp si a x d f a sin l awhich is The reacting mixture is stirred vigorously and p l of h n 1 8continued atalytic its temperature is preferably maintained below 35activity at reduced temperatures. 10 C. There is now added 34.5 grams ofsodium 9 The amount of poisoning impurity retained by hypochlorite(NaOCl) in 10 per cent solution,

- the oxides of the P ior art is no p i e of and the mixtureis stirredfor ten minutes, after exact quantitative determination by presentanwhich it is diluted and the precipitate washed y fl m and the amountnecessary 11 several times by decantation with distilled water,

' render it ineflicient may, and probably does, vary to remove themechanically-bound impurities as 9 according tothe impurity.Consequently it is not far as possible, and" the oxide is then treatedto i le to state precise limits below which the reduce the adsorbedpoisoning impurities, ch10.- impurity must be removed to produce thecata-\ rides in this case, below the tolerable limit. I lysts accordingto the invention, and in the abhave found that a very' satisfactorymanner of sence of exact knowledge, this characteristic of doing this isto wash the oxide with a solution 100 h a a yst s d fi d t be t r ntacontaining a substance which willdisplace the less than the tolerablelimit of poisoning imadsorbed poisoning impurities and which willitpurities, it being evident from what has been self be harmless. -Inmost cases this is best acsaid'of my invention, that, if the tolerablelimit complished by using the nitrate of the metal is surpassed, theinefllcient catalysts of the prior whose oxide is being purified, thenitrate radical 1.5

- are are'produced. pausing desorption of the adsorbfd chloride ion Theproper-state of purity, as embraced in the and itself being adsorbedand, upon hearing, foregoing definition, however, can readily bedeforming oxide, thus giving no undesirable imtermined experimentallyina simple manner by purity in the final product. In this case the meansknown toworkers in the art; when the oxide is washed with a solutionofcobalt nitrate in distilled water until the wash solution after several.days contact with the oxide shows no trace of chlorides. It is thenfiltered and sucked dry, preferably on a fritted glass filter,transfered to a flask containing concentrated nitric acid solutionsaturated withcobalt nitrate, and allowed to stand for two days, when itis filtered and washed with a fresh portion of the nitric acid solution.Cobalt oxide is appreciably soluble in nitric acid, and one function ofsaturating the acid with cobalt nitrate is to reduce dissolution of theoxide by the acid, and hence to cut down washing losses.

The oxide of cobalt thus prepared gives no test for chlorides whendissolved in nitric acid; when air dried at 100 C. it is brown in color;and on microscopic examination with a dark stage it seems to be hornyand gel-like in structure, indicating a highly porous physical statewhich is desirable in oxide catalysts. The material, either as washed,or subsequently dried at 100 C. is placed in a glass tube and heated toabout 200 C.', while air or oxygen dried with phosphorous pentoxide ispassed through it. When water ceases to appear in the efiiuent gas theoxide is ready for use. Duringthe heating any cobalt nitrate retained bythe oxide is decomposed to oxide, so that the oxide is wholly .in themanner described in Example 1.

in the foregoing manner is washed repeatedly by decantation withdistilled water until an acid solution of a sample of the oxide gives notest for chlorides, when it is dried at 200 in the manner describedabove. Although the product is as satisfactory as in the precedingexample, the tendency to peptize upon continued washing may cause a lossof some of the material.

Example 3.-A particularly desirable means of preparing the precipitatedoxide in the required state of purity is by electrolytic purification.An especially suitable procedure is to wash out the major portion of themechanically'held impurities and then suspend the oxide in distilledwater in a suitable container in which there are placed two porous cellseach containing water and a suitable electrode, platinum for example.Upon passing a current between the electrodes, the impurities pass from.the oxide into the appropriate cups. It is usually desirable topreliminarily .clean the porous cells by boiling in nitric acid and thenwashing free from acid.

Oxides free from poisoning impurities may be readily prepared in thismanner, and when purified are prepared for use by drying and heatingThis procedure has been found to be very desirable for the preparationof oxides generally in a state of very high purity. It is simple, theelectrolysis may be permitted to run for long periods with very littleattention, there is no loss of material, and it does not requirethesolutions used for washing described in Example 1, and it effectivelyremoves adsorbed impurities.

Example 4.It has previously been proposed of the invention may beproduced also by careful heating of the nitrate in an atmospherecontaining oxygen and water vapor. This is preferably accomplished bypassing a stream of air and water vapor over cobaltous nitrate heated toabout 200 C. in a tube or other suitable container, the water vapor inthe air preferably corresponding to saturation at about 30 C. Ifdesired, the catalyst may be prepared in supported form by saturatingacid washed asbestos, or other suitable carrier, with the nitrate,drying at about 100 C., and igniting as above. The function of thewatervapor is apparently to bring about by hydrolysis the decomposition ofthe nitrate at a lower temperature than is possible in ignition in theabsence of water vapor, and this lowering of the temperature issufficient to prevent the deleterious action of heat which .haspreviously accompanied the preparation of oxides by ignition methods.This procedure is also applicable to the preparation of other oxidescatalytically active at low temperature. It possesses the advantage,that beginning with a pure material there is no contamination by othermaterials, the oxide is produced in the desired finely divided state,and the procedure is simple and inexpensive and results in a catalysthaving the very desirable characteristics described.

It will be observed that a common feature of the methods given is thatthe oxide is prepared in a highly porous state from a cobalt compound,with less than the tolerable limit of poisoning impurities, and that itis dried in a current of oxygen-containing gas at about 200 C. Dried atlower temperatures, 100 C. for example, the oxide does not appear topossess its full activity, and when dried at such low temperatures itappears to be especially susceptible to the harmful action of watervapor. For these low temperature uses the oxide should not be heatedbeyond about 250 C. In the preparation of the oxide by wet methods, itis dried in the absence of water vapor, while inthe thermaldecomposition method of Example 4, water vapor is used. In the lattercase, the oxide may be dried in moisture-free air, if desired ornecessary, after being produced.

In actual use it has been found that the catalyst produced by any of theforegoing materials is perfectly catalytic for the oxidation of carbonmonoxide at reduced temperatures, and it is capable of continuous actionso long as the reactant gases are kept free of moisture. For example a 1per cent mixture of carbon monoxide in air was dried by phosphorouspentoxide and passed at a rate of 100 cc. per minute through about a 10cm. length of the catalyst in a tube having a cross sectional area ofabout 1 sq. cm. Tested in this manner, over a range of temperature from20 C. to 100 C., the oxide of cobalt catalyst converted the carbonmonoxide to carbon dioxide at 100 per cent efficiency. Intermittentlytested over periods up to four weeks, the catalyst gave no indication ofdiminished activity in the range of temperature referred to, and so faras can be observed it will act continuously for an unlimited period whenprotected from moisture.

Tests have demonstrated that the efiiciency and life of the catalyst aredependent to some extent upon the use of dry gases. Thus, if thecatalyst prepared by the method of Example 1 is dried at 110 C. under apressure of 1 mm.

thereafter. Also, when the completely active material described above isused with gases containing water vapor in concentration suflicient toexert a vapor pressure of 0.4 mm.mercury, the efficiency falls off toabout 47 per cent. It is also characteristic of the catalyst that noinduction period is required, even at low temperatures.

When the catalyst has been used under conditions to render it inactivefrom the presence of moisture, or has absorbed Water vapor from theatmosphere, it may be readily revived by heating in a stream of dry airor oxygen, preferably at ,about 200 C.

Catalysts in accordance with the invention may be used to accomplish theoxidation of most of the readily oxidizable gases and vapors, forexample carbon monoxide, ammonia, sulfur dioxide. aldehydes, toluene,etc., by passing them' mixed with oxygen or air through the catalyst ator above about 0 C.

Although the invention has been described with reference to oxide ofcobalt as the preferred embodiment, it may be also applied to oxide ofnickel. Thus, nickelic oxide prepared from the nitrate in accordancewith Example 1, and purifled electrically in the manner described inExample 3, is 100 per cent efficient in oxidizing carbon monoxide attemperatures down to 20 C. although this oxide appears to adsorb some ofthe carbondioxide formed, which may reduce its activity somewhat.Catalytic oxide of nickle according to the invention may be preparedalso by ignition of the nitrate in the manner described for oxide ofcobalt.

According to the provisions of the patent statutes, I have explained theprinciple and mode of operation of my invention and have described whatI now consider to represent its best embodiment. However, I desire tohave it understood that, within the scope of the appended claims theinvention may be practiced otherwise than as specifically described.

I claim:

1. As a new article of manufacture, a low temperature oxidation catalystconsisting of oxide of a metal of the group consisting of cobalt andnickel and capable of oxidizing carbon monoxide completely and for anunlimited time at temperatures as low as minus 20 C. in dry gasatmospheres containing carbon monoxide and oxygen, and prepared byconverting a compound of said metal to oxide containing less than thelimit of poisoning impurities tolerable with production of said activityat low temperatures, and heating said oxide in an oxidizing atmosphereat an elevated temperature not exceeding about 250 C 2. As a new articleof manufacture, a low temperature oxidation catalyst consisting of oxideof a metal of the group consisting of cobalt and nickel prepared bydecomposition of a thermally decomposable compound of said metal at anelevated temperature in an atmosphere of air and water vapor in anamount greater than that normally present in air and sufficient to causedecomposable compound of said metal at an elevated temperaturebelowabout 250 C. in an atmosphere of air saturated with water vapor tocause hydrolysis of the compound, and the catalyst oxidizing carbonmonoxide completely and for an unlimited time at temperatures as low asminus 20 C. in dry gas atmospheres containing carbon monoxide andoxygen.

4. As a new article of manufacture, a low temperature oxidizing catalystconsisting of oxide of cobalt prepared by decomposition of cobaltnitrate at an elevated temperature below about 250 C. in an atmosphereof air containing water vapor equivalent to saturation at 30 C., saidoxide catalytically oxidizing carbon monoxidecompletely and for anunlimited time at temperatures as low as minus 20 C. in dry gasatmospheres containing carbon monoxide and oxygen.

5. A process of preparing an oxidation catalyst for use at lowtemperatures, comprising heating a thermally decomposable compound of ametal of the group consisting of cobalt and nickel at an elevatedtemperature below that at which the compound normally decomposes inordinary dry air, and during said heating contacting the heated compoundwith an atmosphere of air and Water vapor in an amount greater than thatnormally present inair and sumcient to cause hydrolysis of the compound,to thereby decompose the compound below said normal decompositiontemperature, and maintaining said atmosphere until decomposition tooxide is complete, to thereby produce oxide of said metal capable ofoxidizing carbon monoxide completely and for an unlimited time attemperatures as low as minus 20 C. in dry gas atmospheres containingcarbon monoxide and oxygen.

6. A process of preparing an oxidation catalyst for use at lowtemperatures, comprising heating a thermally decomposable compound of ametal of the group consisting of cobalt and nickel at an elevatedtemperature below about 250 C., and during said heating contacting theheated compound with an atmosphere of air and water vapor in an amountgreater than normally present in air and substantially equivalent tosaturation at 30 C. to decompose the compound to oxide at a temperaturebelow that at which the compound decomposes in ordinary dry air,

and maintaining said atmosphere until decomposition to oxide iscomplete, to thereby produce oxide of said metal capable of oxidizingcarbon monoxide completely and for an unlimited time at temperatures aslow as minus 20 C. in dry gas atmospheres containing carbon monoxide andoxygen.

7. A process of preparing an oxidation catalyst for use at lowtemperatures, comprising heating cobalt nitrate at an elevatedtemperature below about 250 C. and during the heating contacting it withan atmosphere of air and water vapor in an amount greater than thatnormally present in air and sufficient to cause hydrolysis of thenitrate, to thereby decompose the nitrate at a temperature below that atwhich it normally decomposes in ordinary dry air, and maintaining saidatmosphere until decomposition to oxide is complete, to thereby producecobalt oxide capable of oxidizing carbon monoxide completely and for anunlimited time at temperatures as low as minus 20 C. in dry gasatmospheres containing carbon monoxide and oxygen.

JOSEPH C. W. FRAZER.

